Projectile-target Systems Research Articles

Optimisation of the Tripathi model using a nuclear reaction cross-section database

Nuclear reaction cross-sections are an essential ingredient to reliable deterministic and stochastic radiation transport codes used for radiation protection in space and heavy-ion therapy applications. A recent study compared the existing literature data compiled within the open-access GSI-ESA-NASA cross-section database to the models implemented in the transport codes most commonly used for radiation protection in space and heavy-ion therapy applications. The outcome of the comparison was that none of the models fit well the experimental data for all projectile-target systems at all energy ranges. Therefore, the literature data were exploited to optimise the Tripathi–Cucinotta–Wilson model as reported in this work. This model is used as default in FLUKA, TRiP, and SpaceTRiP, it is part of the hybrid-Kurotama (HK) model used in particle and heavy ion transport code (PHITS), and it is implemented in Geant4. The consequences of using the proposed Tripathi–Cucinotta–Wilson optimisation in the HK model are also analysed.

Heavy ion fusion of spherical nuclei

We study the experimental and theoretical fusion reactions of compound nuclei synthesized using different projectile-target systems, among which at least one projectile/target nucleus is spherical. The first part of this study analyses the fusion cross sections obtained using different projectile-target combinations in the synthesis of polonium (Po), thorium (Th), and nobelium (No). In the second part of this study, we suggest the fusion reaction to synthesize the superheavy element Z = 122. We select three nuclei, polonium (Po), thorium (Th), and nobelium (No), which are synthesized using various projectile-target combinations. We also investigate fusion reactions such asZr(Pb, 2n)122 . This study may be a milestone in the synthesis of the superheavy element Z = 122.

O18+Se76 elastic and inelastic scattering at 275 MeV

Background: An accurate description of the initial and final state interactions in the O18+Se76 collision is demanded by the NUMEN project. The study of single and double charge exchange nuclear reactions is the main purpose for NUMEN, since these can be used as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. To date, the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for the NUMEN double charge exchange studies are poorly known. The O18+Se76 case, here under study, is particularly relevant due to its connection with the Ge76 neutrinoless double-β decay. Purpose: In this work the authors want to characterize the initial-state interaction for the O18+Se76 reactions at 275 MeV incident energy determining the optical potential and evaluating the effect of couplings with the inelastic scattering on the elastic channel. Methods: The angular distributions of differential cross section were measured in the angular region between 4∘ and 22∘ in the center-of-mass reference frame. The cross sections were compared with theoretical calculations, that adopt different optical potentials. Coupling effects on the elastic channel were determined into the coupled channels formalism. Results: The excitation energy spectrum of the colliding nuclei and the cross section angular distributions were measured with satisfactory energy resolution. The elastic scattering cross section is not well reproduced in the full angular range explored when the optical model approach is adopted. A good agreement is found using coupled channel calculations. The initial state interaction for the O18+Se76 nuclear reactions at 275 MeV is determined. Conclusions: Coupled channels effects are crucial to obtain a good description of the measured elastic and inelastic channels cross sections, even at large transferred momenta where the optical model approach fails in reproducing the experimental data. The role of channel coupling could be relevant also in the analysis of other open reaction channels in the same collision and should be accounted for in double charge exchange analyses as well.Received 19 December 2020Revised 6 October 2021Accepted 10 November 2021DOI:https://doi.org/10.1103/PhysRevC.104.054610©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDirect reactionsLow & intermediate energy heavy-ion reactionsNuclear reactionsNuclear structure & decaysNucleon-nucleon interactionsTransfer reactionsProperties59 ≤ A ≤ 896 ≤ A ≤ 19TechniquesCollective modelsNuclear data analysis & compilationNuclear reaction analysisOptical, coupled-channel & distorted wave modelsSpectrometers & spectroscopic techniquesNuclear Physics

Initial State Interaction for the 20Ne + 130Te and 18O + 116Sn Systems at 15.3 AMeV from Elastic and Inelastic Scattering Measurements

Double charge exchange (DCE) reactions could provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-β decay. To achieve this goal, a detailed description of the reaction mechanism is mandatory. This requires the full characterization of the initial and final-state interactions, which are poorly known for many of the projectile-target systems involved in future DCE studies. Among these, we intend to study the 20Ne + 130Te and 18O + 116Sn systems at 15.3 AMeV, which are particularly relevant due to their connection with the 130Te→130Xe and 116Cd→116Sn double-β decays. We measure the elastic and inelastic scattering cross-section angular distributions and compare them with theoretical calculations performed in the optical model, one-step distorted wave Born approximation, and coupled-channel approaches using the São Paulo double-folding optical potential. A good description of the experimental data in the whole explored range of transferred momenta is obtained provided that couplings with the 21+ states of the projectile and target are explicitly included within the coupled-channel approach. These results are relevant also in the analysis of other quasi-elastic reaction channels in these systems, in which the same couplings should be included.

Ne20+Ge76 elastic and inelastic scattering at 306 MeV

Background: Double charge exchange (DCE) nuclear reactions have recently attracted much interest as tools to provide experimentally driven information about nuclear matrix elements of interest in the context of neutrinoless double-beta decay. In this framework, a good description of the reaction mechanism and a complete knowledge of the initial and final-state interactions are mandatory. Presently, not enough is known about the details of the optical potentials and nuclear response to isospin operators for many of the projectile-target systems proposed for future DCE studies. Among these, the 20Ne + 76Ge DCE reaction is particularly relevant due to its connection with 76Ge double-beta decay. Purpose: We intend to characterize the initial-state interaction for the 20Ne + 76Ge reactions at 306 MeV bombarding energy and determine the optical potential and the role of the couplings between elastic channel and inelastic transitions to the first low-lying excited states. Methods: We determine the experimental elastic and inelastic scattering cross-section angular distributions, compare the theoretical predictions by adopting different models of optical potentials with the experimental data, and evaluate the coupling effect through the comparison of the distorted-wave Born approximation calculations with the coupled channels ones. Results: Optical models fail to describe the elastic angular distribution above the grazing angle (9.4{\deg}). A correction in the geometry to effectively account for deformation of the involved nuclear systems improves the agreement up to about 14{\deg}. Coupled channels effects are crucial to obtain good agreement at large angles in the elastic scattering cross section.

Investigating the Influence of Incomplete Fusion on Complete Fusion of 16 O –Induced Reaction ≈ 3-8 MeV/nucleon

The dynamics of heavy-ion fusion reaction elaborate in the interaction of 1616O "> projectiles with 16165Ho "> and 51 V targets at ≈3-8MeV/nucleon specific energies were studied. This study were emphases on the relationship between entrance channel belongings and incomplete fusion reaction. The experimentally measured excitation functions of various reaction products duplicated by complete or incomplete fusions of 1616O "> + 1651V"> , 16165Ho "> projectile-target systems had been compared and analyzed within the predicted excitation functions, using the statistical model code PACE4. For α-emitting channels in the present systems, the measured excitation functions had been highest than the predictions of the theoretical model code, which may focuses at these energies. However for non-alpha emitting channels in this system the measured excitation function had been nice agreement with the theoretical values. An endeavor were made to nearly the incomplete fusion fraction that designates importance of incomplete fusion process. Keywords: Alpha emitted, CF reaction, Entrance channel, Heavy ion fusion, ICF reaction, Non alpha emitted DOI : 10.7176/APTA/79-03 Publication date :September 30 th 2019

On the universal scaling in the electronic stopping cross section for heavy ion projectiles

ABSTRACTEnergy deposition of heavy ions when penetrating a material is of crucial importance in determining the damage to materials with implications in areas such as material science, plasma physics, radiotherapy and dosimetry. Due to the N-body electron problem, it has been thought that the electronic stopping cross section is unique for a given projectile–target combination and differs from system to system. In this work, we show that within the Bethe theory, there is a universal scaling when the electronic stopping cross sections and projectile kinetic energy are scaled properly in terms of the target mean excitation energy, , for all projectile–target combinations. We show that the scaling is given by as a function of , thus showing the importance of the characterization of the mean excitation energy. The scaling law expresses a systematic and universal behavior among complex projectile–target systems in the energy deposition, characterized by the minimum momentum transfer during the slowing down process. We provide an analytic expression for the universal scaling law for the stopping cross section of any projectile–target combination valid at high collision energies. Finally, we verify the universal scaling law by comparison to atomic and molecular experimental data available in the literature. We expect our findings will motivate further experimental work to verify our universal scaling for more complex systems in the absence of experimental data.

Projectile fragment emission angles in fragmentation reactions of light heavy ions in the energy region <200 MeV/nucleon: Experimental study

Measurements of fragment emission angles for 57 and 93 MeV/nucleon C-12 and 95 MeV/nucleon O-16 projectiles in graphite, Plexiglas and polyethylene targets were performed using trajectory tracing technique with CR-39 detectors. The results were compared with calculations with the fragment emission angle model (FRANG). The angular resolution of the measurements was achieved to be <0.1 degrees. The measured fragment emission angles imply that the generally accepted straight-ahead approximation of fragment emissions in nuclear collisions is oversimplified as the fragments are clearly emitted at different angles related to the primary particles. The calculated values were in agreement with the experimental ones within the margin of a few degrees for most of the examined projectile-target systems. However, some discrepancies were observed. Thus a new calculation was performed with a modified version of the model M-FRANG. For both FRANG and M-FRANG, chai-square values were calculated to test the degree of agreement with our measurements. It was confirmed that the M-FRANG showed better agreement despite its simplicity, and it was established it can be successfully used in several applications, including simple and fast test of more complicated 3D particle and heavy ion transport codes.

Energy-dependent optical model potentials for α and deuteron with 12C

Energy-dependent phenomenological optical model potentials based on a single-folding model approach for the α-12C and deuteron-12C systems were obtained for incident energies between 10 and 100 MeV/nucleon. The Lane-consistent Bruyères Jeukenne–Lejeune–Mahaux model nucleon–nucleus potentials were used in these calculations. With only three free parameters, these potentials account satisfactorily for both angular distributions of elastic scattering cross sections and total reaction cross sections of both projectile–target systems within the energy range studied. Comparisons were made between the present potentials and other systematic phenomenological potentials.

α-decay and fusion phenomena in heavy ion collisions using nucleon-nucleon interactions derived from relativistic mean-field theory

Nucleus-nucleus potentials are determined in the framework of the double-folding model for a new microscopic nucleon-nucleon (NN) interaction relativistic mean field-3-Yukawa (R3Y) derived from the popular relativistic mean-field theory Lagrangian, and the results are compared for the use of Michigan-3-Yukawa (M3Y) effective NN interactions. The double-folding potentials so obtained are further taken up in the context of the preformed cluster model (PCM) of Gupta and collaborators and the barrier penetration model to study respectively the ground-state (g.s.) {alpha}-decay and low-energy fusion reactions. In this paper, using PCM, we deduce empirically the {alpha} preformation probability P{sub 0}{sup {alpha}(emp)} from experimental data on a few g.s. {alpha} decays in the trans-lead region. For fusion reactions, two projectile-target systems {sup 12}C+{sup 208}Pb and {sup 16}O+{sup 208}Pb are selected for calculating the barrier energies as well positions, fusion cross sections ({sigma}{sub fus}), and fusion barrier distribution [D(E{sub c.m.})]. The barrier energies and positions change for the R3Y NN interactions in comparison with those of the M3Y NN interactions. We find that in the {alpha}-decay studies the values of P{sub 0}{sup {alpha}(emp)}(R3Y) are similar to those of P{sub 0}{sup {alpha}(emp)}(M3Y). Further, both NN interactions give similar {sigma}{sub fus} values using the Wong formula specifically when more » the R3Y NN interaction calculated {sigma}{sub fus} values are reduced by 1.5 times, and the results are in agreement with the experimental data for both the systems, especially for the higher energies. Results for D(E{sub c.m.}) are also quite similar for both choices of NN interaction. « less

Reaction mechanism in the20Ne+59Co system at 3--7 MeV/nucleon, and observation of entrance-channel mass-asymmetry of the incomplete fusion fraction

Incomplete fusion of $^{20}\mathrm{Ne}$ with $^{59}\mathrm{Co}$ has been investigated at 3--7 MeV/nucleon using the measurement and analysis of excitation functions. The recoil-catcher technique followed by offline gamma-ray spectroscopy has been employed. Evaporation residues are found to have contributions from precursor decays, which have been separated out from the measured cumulative cross sections of evaporation residues. Measured independent cross sections are compared with PACE-2 predictions. The PACE-2 calculations are carried out for evaporation residues formed in complete fusion (CF), and the parameters are optimized so as to reproduce the cross section of evaporation residues produced exclusively in CF, e.g., $\mathit{xn}$ and pxn products. With these parameters, the predicted CF cross sections for alpha emission products are calculated. Any substantial enhancement in the experimental cross section over the PACE-2 prediction is taken as a signature of incomplete fusion (ICF). The analysis indicates the occurrence of incomplete fusion involving the breakup of $^{20}\mathrm{Ne}$ into $^{16}\mathrm{O}$ $+$ $^{4}\mathrm{He}$ and/or $^{12}\mathrm{C}$ $+$ $^{8}\mathrm{Be}$(2\ensuremath{\alpha}) followed by fusion of one of the fragments with the target nucleus $^{59}\mathrm{Co}$. These data also suggest that the probability of incomplete fusion increases with the projectile energy. Moreover, the ICF probability is found to increase with entrance-channel mass-asymmetry of the projectile-target systems.

Projectilelike fragment emission angles in fragmentation reactions of light heavy ionsin the energy region 200MeV∕nucleon: Modeling and simulations

A new semiempirical model called FRANG for calculation of fragment emission angles in light and heavy ion fragmentation reactions was developed. Contributions from both central and peripheral collisions were investigated, where fragmentation occurs due to nuclear and Coulomb interaction, respectively. For central collisions the reaction was described by a two step abrasion-ablation model, where collision parameters were determined from a simple geometrical model. The fragment emission angles were calculated using a parametrization of longitudinal momentum loss and transverse momentum uptake in the collision of projectile and target atom. For peripheral collisions the Coulomb excitation of nucleon vibration resonances and subsequent decay into fragments was taken into account. Fragment emission angles were calculated from deflection in the electric field and from the amplitude of vibrations in excited nuclear states. The modeled emission angles were in accordance with the experimental values for most projectile-target systems examined and compared. It was established that the model very well reproduces the experimental results in the energy region $&lt;200\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\text{nucleon}$, despite its simplicity, and can be successfully employed in several applications. The model is estimated to be valid in the energy range from a few $10\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\text{nucleon}$ up to few $100\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}∕\text{nucleon}$.

Recent studies in heavy ion induced fission reactions

Nuclear fission process involves large scale shape changes of the nucleus, while it evolves from a nearly spherical configuration to two separated fission fragments. The dynamics of these shape changes in the nuclear many body system is governed by a strong interplay of the collective and single particle degrees of freedom. With the availability of heavy ion accelerators, there has been an impetus to study the nuclear dynamics through the investigations of nucleus-nucleus collisions involving fusion and fission process. From the various investigations carried out in the past years, it is now well recognized that there is large scale damping of collective modes in heavy ion induced fission reactions, which in other words implies that nuclear motion is highly viscous. In recent years, there have been many experimental observations in heavy ion induced fission reactions at medium bombarding energies, which suggest possible occurrence of various non-equilibrium modes of fission such as quasi-fission, fast fission and pre-equilibrium fission, where some of the internal degrees of freedom of the nucleus is not fully equilibrated. We have carried out extensive investigations on the fission fragment angular distributions at near barrier bombarding energies using heavy fissile targets. The measured fragment anisotropies when compared with the standard saddle point model (SSPM) calculations show that for projectile-target systems having zero or low ground state spins, the angular anisotropy exhibits a peak-like behaviour at the sub barrier energies, which cannot be explained by the SSPM calculations. For projectiles or targets with large ground state spins, the anomalous peaking gets washed out due to smearing of the K-distribution by the intrinsic entrance channel spins. Recently studies have been carried out on the spin distributions of fission fragments through the gamma ray multiplicity measurements. The fission fragments acquire spin mainly from two sources: (i) due to rigid rotation of the nascent fragments at scission and (ii) due to statistical excitation of the spin bearing collective modes in the fissioning nucleus. One of the collective modes — the tilting mode depends on the K quantum number and is responsible for the emission angle dependence of fragment spin. In our studies, we have shown conclusively that the collective statistical spin modes get strongly suppressed for high K values corresponding to large rotational frequencies along the fission axis. These results bring out the importance of the dynamical effects in the heavy ion induced fusion-fission reactions. The present article will review the work carried out on the above aspects in heavy ion fission reactions as well as on the fission time scales, and some of the recent studies on the mass-energy correlations of fission fragments at near-barrier bombarding energies.

L-shell filling ofN6+andO7+ions from a clean and LiF-covered Au(111) surface

We report on a high-resolution Auger spectroscopy study of the interaction of ${\mathrm{N}}^{6+}$ and ${\mathrm{O}}^{7+}$ ions with a clean and a LiF-covered Au(111) target. The electron spectra from collisions on Au(111) and LiF-covered Au(111) are distinctly different. The ones resulting from the interaction with Au(111) covered with one monolayer of LiF resemble spectra taken on bulk LiF, which, in contrast to LiF-covered Au(111), is an insulator. On the Au(111) surface and for scattering geometries preventing projectile penetration below the first atomic layer, a more efficient L-shell filling for ${\mathrm{O}}^{7+}$ than for ${\mathrm{N}}^{6+}$ ions is observed. Surprisingly enough, for a single monolayer of LiF on Au the total K Auger intensity of nitrogen is nearly 30$%$ larger as compared to the clean Au(111) target, while for oxygen no enhancement is found. These findings demonstrate that, for specific projectile-target systems (e.g., N-LiF), an efficient mechanism that fills the projectile L shell is active well before the projectiles reach the surface, so that $\mathrm{KLL}$ electrons are emitted at an early stage of the interaction.

Effect of multiparticle collisions on pion production in relativistic heavy-ion reactions

In the present work we discuss the effect of N-body processes on pion multiplicity in relativistic heavy-ion reactions. This effect is analyzed in the energy range from the pion threshold up to 2 GeV/nucleon, for several projectile-target systems. The analysis is carried out in the context of intranuclear cascade calculations. It is shown that the inclusion of multibaryonic collisions is a crucial element in the study of the pion production mechanisms, being strongly dependent on the adopted correlation range for the particles involved in the N-body processes. {copyright} {ital 1997} {ital The American Physical Society}

Electron-electron interaction and two-center effects in projectile ionization at backward emission angles.

We analyze the electron emission spectrum into backward angles for projectile ionization in 0.5-MeV/u ${\mathrm{H}}^{0}$ and ${\mathrm{He}}^{+}$ on He collisions. The energy and angular distributions of the ejected electron are calculated taking into account both scattering correlations and two-center effects. Two-center effects are treated using the continuum-distorted-wave approximation and the classical-trajectory Monte Carlo method. Correlation effects are described in terms of a Born series including contributions up to second order. Both contributions are found to enhance significantly the electron-loss cross section in near-symmetric projectile-target collision systems. We find improved agreement with experiment for ${\mathrm{He}}^{+}$ on He collisions. Extensions to heavier targets are also discussed.

Multiple angular scattering of heavy ions ( 16,17O, 40Ar, 86Kr and 100Mo) at intermediate energies (20–90 MeV/u)

An original experimental method has been developed using the LISE magnetic spectrometer at the GANIL accelerator for measuring the angular distributions of heavy ions at the exit of targets. Multiple angular scattering of heavy ions ( 16,17O, 40Ar, 86Kr and 100Mo) in solid and gaseous media have thus been measured in the energy range 20–90 MeV/u. With these different projectile-target systems and incident energies the Born parameter α B takes values in a wide range (0.5–100). The experimental results have thus been compared to multiple scattering theories based on classical or quantum mechanical calculations. As far as the classical theory is concerned a “universal” relation links the reduced straggling angle \\ ̃ ga 1 2 and the reduced thickness τ intr Meyer according to the expression \\ ∼ ga 1 2 = 1.00 τ 0.55 . In the framework of the quantal Molière theory a good agreement is fou experiment when α B is approximately unity. Increasing deviations are observed when this parameter increases up to 100.

Direct ionization and capture in inner-shell processes

Direct ionization (DI) and electron capture (EC) contributions have been inferred from target X-ray cross sections. Measurements have been made for the K-, L-, and M-shells for a range of selected projectile-target systems and ion-target electron velocity ratios. The inferred DI and EC results have been compared to Coulomb ionization theories consisting of the first Born and the perturbed stationary state (PSS) approaches. The comparison provides evidence of the validity of the PSS theory for the range of projectile-target systems and velocity ratios studied.

Excitation functions for production of heavy actinides from interactions ofO18withCm248andCf249

Excitation functions have been measured for the production of isotopes of Bk through Fm in bombardments of $^{248}\mathrm{Cm}$ with 97- to 122-MeV $^{18}\mathrm{O}$ ions and of isotopes of Bk through No in bombardments of $^{249}\mathrm{Cf}$ with 91- to 150-MeV $^{18}\mathrm{O}$ ions. The cross sections and widths of the mass distributions for the actinides produced in these reactions are very similar for transfer of the same numbers of nucleons. A semiquantitative comparison of the experimental results with calculations based on a simple model shows that calculations of this type are helpful in selection of projectile-target systems and optimum energies for production of specific actinide isotopes and for synthesis of as yet unknown heavy isotopes and elements. Comparisons of experimental results with calculations show that, in general, about half of the kinetic energy of the projectile is transferred to the actinide product.NUCLEAR REACTIONS $^{248}\mathrm{Cm}(^{18}\mathrm{O}, X)$, $E(^{18}\mathrm{O})=97, 104, 113, 122$ MeV; $^{249}\mathrm{Cf}(^{18}\mathrm{O}, X)$, $E(^{18}\mathrm{O})=91, 97, 104, 113, 122, 150$ MeV; measured $\ensuremath{\sigma}$ and isotopic distributions for $Z=97\ensuremath{-}102$.

Charge transfer prior to fusion

In reactions between very asymmetric projectile-target systems charge is preferably transferred from the lighter to the heavier nucleus. This leads to a decrease of the potential barrier between the nuclei and increase of the fusion cross-section. We perform trajectory calculations with energy dissipation and proton transfer to estimate the magnitude of the effect.